Data Transformation

Letter abbreviations:
- <int> stands for integers.
- <dbl> stands for real numbers.
- <chr> stands for character vectors.
- <dttm> stands for date-times.

View(nycflights13::flights)

5.2.4 Exercises

1a.

filter(flights,arr_delay >= 120)

1b.

filter(flights,dest %in% c("IAH","HOU"))

1c.

filter(flights, carrier %in% c("AA","DL","UA"))

1d.

filter(flights, month %in% 7:9)

1e.

filter(flights, arr_delay > 120, dep_delay <= 0)

1f.

filter(flights, dep_delay >= 60, (dep_delay - arr_delay > 30))

1g.

filter(flights, dep_time >= 2400 | dep_time <= 600)

2. <between> is a shortcut for a<=x<=b.

filter(flights, between(dep_time, 600 ,2400))

sum(is.na(flights$dep_time))

[1] 8255

map_dbl(flights, ~ sum(is.na(.x)))

          year          month 
             0              0 
           day       dep_time 
             0           8255 
sched_dep_time      dep_delay 
             0           8255 
      arr_time sched_arr_time 
          8713              0 
     arr_delay        carrier 
          9430              0 
        flight        tailnum 
             0           2512 
        origin           dest 
             0              0 
      air_time       distance 
          9430              0 
          hour         minute 
             0              0 
     time_hour 
             0 

Airtime, arr_delay, dep_delay and tail number have missing values.

4. Unsure

5.3.1 Exercises

1. Unsure
   

arrange(flights, dep_delay)

arrange(flights, desc(dep_delay))

arrange(flights, air_time)

# Shortest
flights %>%
  arrange(air_time) %>%
  select(flight, air_time)

# Fastest
flights %>%
  arrange(-air_time) %>%
  select(flight, air_time)

5.4.1 Exercises

select(flights, dep_time, dep_delay, arr_time, arr_delay)
select(flights, starts_with("dep"), starts_with("arr"))
select_(flights, "dep_time", "dep_delay", "arr_time", "arr_delay")

select(flights, arr_delay,arr_delay)

Nothing, only returns once.

vars <- c("year", "month", "day", "dep_delay", "arr_delay")
select(flights, one_of(vars))

Unsure why helpful.

select(flights, contains("TIME"))

Unsure.